In order to improve the preservability of foods, various kinds of preservatives have been used. Examples of these preservatives are synthetic preservatives such as sodium propionate, calcium propionate; acids such as acetic acid; and alcohols. However, it has been apt to be restricted by law to apply synthetic preservatives to foods. Addition of acetic acid to food is disadvantageous in that acidity is caused to occur in the food and its pH value is lowered to spoil the quality of the food. Similarly, alcohols when they are added to food in an amount enough to bring about sufficient antiseptic effect, give to the food an alcoholic smell and cause loss of original flavour of said food.
There have been disclosed in some Published unexamined patent applications (Kokai tokkyo koho) some methods for conquering the above-mentioned defects. These methods are similar in that a solution prepared by adding one or more of materials selected from the group consisting of egg shell, sodium bicarbonate and sodium hydroxide to a vinegar in a certain ratio, is applied to a specific food to be added. Examples of these patent applications are as follows; Published unexamined patent applications (Kokai tokkyo koho) (hereinafter referred to as P.U.P.A.) No. 15847/77 (laid open, Feb. 5, 1977; Seasoned nameko), P.U.P.A. No. 15849/77 (laid open, Feb. 5, 1977; Gelidium jelly), P.U.P.A. No. 21341/77 (laid open, Feb. 17, 1977; Gyoza), P.U.P.A. No. 21360/77 (laid open, Feb. 17, 1977; Grilled egg), P.U.P.A. No. 21399/77 (laid open, Feb. 17, 1977; Miso), P.U.P.A. No. 34952/77 (laid open, Mar. 17, 1977; Fresh fermented pickles), P.U.P.A. No. 34953/77 (laid open, Mar. 17, 1977; Processed octopus), P.U.P.A. No. 90643/77 (laid open, July 30, 1977; Noodles), P.U.P.A. No. 99294/77 (laid open, Aug. 19, 1977; Mirin seasonings), P.U.P.A. No. 145551/77 (laid open, Dec. 3, 1977; Grated ginger), P.U.P.A. No. 148698/77 (laid open, Dec. 10, 1977; Soy), P.U.P.A. No. 96341/78 (laid open, Aug. 23, 1978; Noodles), and P.U.P.A. No. 96350/78 (laid open, Aug. 23, 1978; Fresh fermented pickles).
However, these prior art methods have been determined for and invented independently for different kinds of foods so that said solution can be effectively applied to the food concerned with their invention. Consequently, these prior art methods do not show anything about whether said solution is also effective for foods other than in their invention and under what conditions said solution is applicable for other kinds of foods. Foods are diversified in their materials, and it is well known that various food products can be made when the processing is carried out under different conditions, even though they started from the same materials. Accordingly, it is necessary to use "Trial and Error Procedure" for determining foods to which some preservatives are applicable as well as the way how to apply these preservatives.